SUBROUTINE ZTRTI2( UPLO, DIAG, N, A, LDA, INFO ) * * -- LAPACK routine (version 3.2) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2006 * * .. Scalar Arguments .. CHARACTER DIAG, UPLO INTEGER INFO, LDA, N * .. * .. Array Arguments .. COMPLEX*16 A( LDA, * ) * .. * * Purpose * ======= * * ZTRTI2 computes the inverse of a complex upper or lower triangular * matrix. * * This is the Level 2 BLAS version of the algorithm. * * Arguments * ========= * * UPLO (input) CHARACTER*1 * Specifies whether the matrix A is upper or lower triangular. * = 'U': Upper triangular * = 'L': Lower triangular * * DIAG (input) CHARACTER*1 * Specifies whether or not the matrix A is unit triangular. * = 'N': Non-unit triangular * = 'U': Unit triangular * * N (input) INTEGER * The order of the matrix A. N >= 0. * * A (input/output) COMPLEX*16 array, dimension (LDA,N) * On entry, the triangular matrix A. If UPLO = 'U', the * leading n by n upper triangular part of the array A contains * the upper triangular matrix, and the strictly lower * triangular part of A is not referenced. If UPLO = 'L', the * leading n by n lower triangular part of the array A contains * the lower triangular matrix, and the strictly upper * triangular part of A is not referenced. If DIAG = 'U', the * diagonal elements of A are also not referenced and are * assumed to be 1. * * On exit, the (triangular) inverse of the original matrix, in * the same storage format. * * LDA (input) INTEGER * The leading dimension of the array A. LDA >= max(1,N). * * INFO (output) INTEGER * = 0: successful exit * < 0: if INFO = -k, the k-th argument had an illegal value * * ===================================================================== * * .. Parameters .. COMPLEX*16 ONE PARAMETER ( ONE = ( 1.0D+0, 0.0D+0 ) ) * .. * .. Local Scalars .. LOGICAL NOUNIT, UPPER INTEGER J COMPLEX*16 AJJ * .. * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. * .. External Subroutines .. EXTERNAL XERBLA, ZSCAL, ZTRMV * .. * .. Intrinsic Functions .. INTRINSIC MAX * .. * .. Executable Statements .. * * Test the input parameters. * INFO = 0 UPPER = LSAME( UPLO, 'U' ) NOUNIT = LSAME( DIAG, 'N' ) IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN INFO = -1 ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN INFO = -2 ELSE IF( N.LT.0 ) THEN INFO = -3 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN INFO = -5 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'ZTRTI2', -INFO ) RETURN END IF * IF( UPPER ) THEN * * Compute inverse of upper triangular matrix. * DO 10 J = 1, N IF( NOUNIT ) THEN A( J, J ) = ONE / A( J, J ) AJJ = -A( J, J ) ELSE AJJ = -ONE END IF * * Compute elements 1:j-1 of j-th column. * CALL ZTRMV( 'Upper', 'No transpose', DIAG, J-1, A, LDA, $ A( 1, J ), 1 ) CALL ZSCAL( J-1, AJJ, A( 1, J ), 1 ) 10 CONTINUE ELSE * * Compute inverse of lower triangular matrix. * DO 20 J = N, 1, -1 IF( NOUNIT ) THEN A( J, J ) = ONE / A( J, J ) AJJ = -A( J, J ) ELSE AJJ = -ONE END IF IF( J.LT.N ) THEN * * Compute elements j+1:n of j-th column. * CALL ZTRMV( 'Lower', 'No transpose', DIAG, N-J, $ A( J+1, J+1 ), LDA, A( J+1, J ), 1 ) CALL ZSCAL( N-J, AJJ, A( J+1, J ), 1 ) END IF 20 CONTINUE END IF * RETURN * * End of ZTRTI2 * END